Effects of methoxychlor treatment of pregnant mice on female offspring of the treated and subsequent pregnancies.

This study was designed to assess whether exposure to the estrogenic pesticide methoxychlor (MXC) during pregnancy would affect reproductive parameters not only in female offspring exposed prenatally, but also in those of a subsequent litter. Mice were exposed via oral gavage to 7.5, 5.0, or 2.5 mg technical grade MXC (50%) or 0.025 mg estradiol-17 beta (E-17 beta) from days 6 to 15 of pregnancy. Following delivery, female offspring (F1a) were cross-fostered and sacrificed at 8 weeks of age. Mothers exposed during their first pregnancy were allowed to mate again and their second set of offspring (F1b) were similarly evaluated to detect any latent effects from the initial exposure. Mice exposed to 7.5 mg MXC were unable to carry their litters to term. Results revealed a significant increase in the length of gestation of mice exposed to both E-17 beta and 5.0 mg MXC. A larger percentage of atretic follicles appeared in the ovaries of F1a females exposed prenatally to 5.0 mg MXC when compared to controls. Females from the F1b litter displayed a significant advance in time of vaginal opening, an apparent residual effect of MXC from a mother exposed during a previous pregnancy.